A vehicle driveline may produce torque at an engine and transfer the engine torque to vehicle wheels through a step ratio transmission. As vehicle speed increases, the step ratio transmission may engage a first gear and disengage a second gear in order to operate the engine in a desired speed range. A first clutch may open to release the first gear and a second clutch may close to engage the second gear. If the transmission is upshifting, the transmission provides a first torque ratio in the first gear that is higher than a second torque ratio provided by the transmission while engaged in the second gear. Consequently, if engine torque is maintained constant throughout a gear shift, there may be a drop in wheel torque that results from entering the new gear (e.g., the second gear). The drop in observed wheel torque may be described as a “torque hole,” and the drop in wheel torque may be particularly noticeable during the shift when the off-going clutch is being released and the on-coming clutch is being applied. Thus, it may be desirable to operate the driveline in a way that provides a near constant rate of acceleration so that vehicle drivability may be improved.
The inventors herein have recognized the above-mentioned issues and have developed a driveline operating method, comprising: during a first condition, adjusting a transmission input torque actuator during a power-on upshift torque transfer phase via a controller in response to a transmission instantaneous lower input torque threshold, the transmission instantaneous lower input torque threshold responsive to torque capacity of an on-coming clutch, a torque ratio of a transmission engaged in a first gear, and a torque ratio of the transmission engaged in a second gear.
By adjusting a transmission input torque actuator during a power-on upshift, it may be possible to fill a torque hole that may occur during a torque transfer phase of a power-on upshift when an off-going clutch is being released and an on-coming clutch is being applied. In particular, increasing the transmission input torque may improve wheel torque delivery by transferring transmission input torque through the old gear that is being disengaged and the new gear being engaged. The transmission input torque may be increased via increasing torque output of an engine, an integrated starter/generator, or the engine and the integrated starter generator.
The present description may provide several advantages. For example, the approach may provide for smooth torque delivery from an engine to vehicle wheels. Further, the approach also provides for adjusting output of a rear drive unit electric machine to compensate for torque disturbances that may occur during power-on upshifts. In addition, the torque capacity of an on-coming clutch may be adjusted during the torque transfer phase and inertia phases of the power-on upshift to improve shift smoothness and torque transfer between torque sources in a vehicle driveline.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.